Polyamine is a general term for those alkylamines with two or more amino groups. There are four types of polyamines [putrescine (H2N(CH2)4NH2), cadaverine (H2N(CH2)5NH2), spermidine (H2N(CH2)4NH(CH2)3NH2) and spermine (H2N(CH2)3NH(CH2)4NH(CH2)3NH2)] and acetylated forms thereof in the human body.
Relatively recently, it was found that two types of diacetylpolyamines [N1,N8-diacetylspermidine (hereinafter expressed as “DiAcSpd”) and N1,N12-diacetylspermine (hereinafter expressed as “DiAcSpm”)] are excreted in urine though very small in quantities. While these components occupy only 1.4% and 0.6% of the total polyamine, respectively, in the urine of healthy persons, the ratios of these components remarkably increase in the urine of cancer patients as compared to other polyamine components. Further, it has been shown that these components also have other characteristics of tumor markers (Sugimoto, M. et al., J. Cancer Res. Clin. Oncol., 121, 317-319 (1995); Hiramatsu, K. et al., J. Cancer Res. Clin. Oncol., 123, 539-545 (1997)).
Initially, DiAcSpd and DiAcSpm were quantitatively determined by a method which is a combination of a fractionation measuring system by HPLC and a detection system using enzyme (Hiramatsu, K. et al., J. Biochem., 117, 107-112 (1995)). However, more simple measuring methods have been developed. In particular, with respect to the measurement of DiAcSpm, an ELISA method using a specific antibody was developed recently (Hiramatsu, K. et al., J. Biochem., 124, 231-236 (1998)).
Recently, Fujiwara et al. prepared monoclonal antibodies to DiAcSpm (Japanese Unexamined Patent Publication No. H11-75839). With these antibodies, 50% binding inhibition activity against immunoreaction with DiAcSpm is only about 100 times as much as 50% binding inhibition activity against immunoreaction with N1-acetylspermidine (hereinafter expressed as “N1-AcSpd”) and is only about 20 times as much as 50% binding inhibition activity against immunoreaction with N1-acetylspermine (hereinafter expressed as “N1-AcSpm”) which is a monoacetylated form of spermine. Since the amount of N1-AcSpd in the urine of healthy persons is about 25 times as much as the amount of DiAcSpm therein, the crossreactivity of the above antibody with N1-AcSpd in the urine of healthy persons is 25 when the crossreactivity of the antibody with DiAcSpm therein is taken as 100. Therefore, the antibody may yield false-positive results. Accordingly, in order to enhance the measuring sensitivity for DiAcSpm, a DiAcSpm-specific monoclonal antibody whose crossreactivities with N1-AcSpd and N8-acetylspermidine (hereinafter expressed as “N8-AcSpd”) are still lower is required.